Effect of Heat Stress on the Photosynthetic Characteristics in Flag Leaves at the Grain‐Filling Stage of Different Heat‐Resistant Winter Wheat Varieties

Abstract

AbstractHeat stress has become an increasingly important factor in limiting wheat yields. In northernChina, high temperature (>30 °C) during the grain filling is one of the major constraints in increasing wheat productivity. We used two winter wheat (Triticum aestivumL.) cultivars with different sensitivities to heat stress (Jimai 22 ‘JM22’, low sensitivity and Xinmai 26 ‘XM26’, high sensitivity) to study the various aspects of photosynthetic characteristics during the grain filling stage under heat stress. The results showed that photosynthesis rates (Pn) in flag leaves ofXM26 decreased faster than inJM22 under heat stress during the grain‐filling stage.Pndecreased more rapidly under heat stress than without stress, by up to 69.9% and 59.3%, respectively, at 10 days following heat stress (10DAS). This decline ofPnwas not caused by heat‐induced stomatal limitation, but rather by a decline in Rubisco activity and a functional drop in photosystemII(PSII). After heat stress, the grain yield ofJM22 decreased by 6.41%, butXM26 decreased by 11.43%, when compared with their respective controls. Heat stress also caused an alteration of mesophyll cell ultrastructure. Injury caused by heat stress to organelles inXM26 was more severe thanJM22. Moreover, theJM22 cultivar showed some self‐repair capacity following heat stress injury. These results indicate that declines in photosynthetic performance caused by heat stress were cultivar‐dependent. Compared withXM26, theJM22 cultivar had superior heat stability in terms ofPSIIfunction and carboxylation activity, both of which are susceptible to heat stress.